html, body {
    margin: 0;
    padding: 0;
    width: 100%;
    height: 100%;
    -moz-user-select: none;
    user-select: none;
}

main {
    width: 400px;
    margin: 20px auto;
}

main div {
    float: left;
    width: 80px;
    height: 80px;
    margin: 10px;
    cursor: pointer;
    color: transparent;
    font-size: 20px;
    font-weight: bold;
    text-align: center;
    line-height: 80px;
    vertical-align: middle;
    background-color: wheat;
    border-radius: 10px;
}

.fliped {
    color: white;
    background-color: #dd5862;
}

.matched {
    color: gray;
    background-color: lightgray;
}

@media (max-width: 400px) {

    main { width: 100%; }
    
    main div {
        width: 20%;
        margin: 2.5%;
    }
}